The present invention relates to a thermosetting resin and a method for producing the same.
Aminoplast resins and phenol resins have conventionally been used as thermosetting resins (impregnating resin compositions or adhesive resin compositions for building materials) for use in laminate sheets such as decorative laminated sheets and WPC (wood-plastic combination) sheets.
However, these conventional thermosetting resins are stiff but brittle, lack flexibility and toughness, are inferior in bending flexibility. When they are used as resins for paper impregnation in manufacture of decorative laminated sheets, for example, they split easily upon bending.
In manufacture of laminated sheets such as WPC sheets, paper is impregnated with the thermosetting resins, and the resulting impregnated paper is used as an adhesive layer between wood and wood or between a plastic and wood. However, the adhesive layer lacks flexibility and highly shrinks by heat to thereby invite the resulting product to warp.
Consequently, many proposals have been made to improve these properties of stiffness, brittleness and heat-shrinkable properties. For example, a process for improving physical properties has been proposed. In the process, a terminal group of a melamine resin is subjected to acrylic-modification or allyl-modification to thereby impart a double bond thereto, and the terminal double bond undergoes radical polymerization to thereby improve the physical properties of the resulting resin, such as toughness and flexibility. However, the acrylic-modified melamine resin is sensitive to light or heat, becomes excessively reactive and thereby has poor stability. In addition, the resin cannot be satisfactorily diluted with water, has thereby very poor workability and must be improved in these properties. The process in which a double bond derived from an allyl ether is introduced by allyl-modification does not effectively impart flexibility to a melamine resin and is insufficiently effective for improvement of the properties of stiffness and brittleness of the melamine resin, although it can improve the stability and diluting property with water of the acrylic-modified melamine resin.
To positively improve the properties of stiffness and brittleness of the melamine resins and other thermosetting resins, a process has been proposed in which an emulsion of a polymer such as an acrylic polymer or poly(vinyl acetate) is added to the thermosetting resins. However, the resulting resins have markedly decreased adhesive strength, water resistance, and moisture resistance and cannot be used in practice specifically as adhesives, although the process exhibits some effects upon improvement of the properties of stiffness and brittleness of the aminoplast resins.
When phenol resins are used in these applications, they are very slowly cured and have poor workability as compared with the aminoplast resins. In addition, the phenol resins are also stiff and brittle as in the aminoplast resins, lack flexibility and impact resistance and invite discoloration of paper impregnated with the resins.
Separately, a technique has been proposed in which textile products are subjected to treatment with a resin using an aqueous solution containing an aminoplast resin, a diol surfactant and an acidic crosslinking catalyst (Japanese Unexamined Patent Application Publication No. 55-132777). However, the resulting products obtained by this technique have poor water resistance. In addition, when the aqueous solution is used as an adhesive resin composition for use in building materials such as decorative laminated sheets and WPC, the adhesive resin composition cannot satisfactorily be used in practice. When the aqueous solution is used as a resin composition for impregnating reinforcing materials or fillers such as center materials used for making tatami mats, the resulting composition has problems in its performances.
Another technique has been proposed in which an aminoplast resin is subjected to a condensation reaction with an alcohol having a polyethylene oxide chain by heating at 50xc2x0 C. to 150xc2x0 C. under strongly acidic conditions, and the resulting resin is applied to paper or a cloth for resin treatment (Japanese Unexamined Patent Application Publication No. 56-37399). However, the condensation reaction is highly reactive and cannot significantly be controlled. In this connection, the resulting resin in question can be used for imparting hydrophilicity to materials such as paper or cloths, for providing a smooth texture and for use as an antistatic agent, thus exhibiting some advantages. However, the resulting products show decreased water resistance and strength at high humidity, and have insufficient rigidity. Accordingly, the resin in question has low practical utility as an impregnating resin composition for impregnating reinforcing materials or fillers or an adhesive resin composition for use in building materials. As thus described, there are many proposals for imparting flexibility to aminoplast resins or for improving shrink properties thereof. However, some of them cannot sufficiently improve the properties, and the others invite insufficient performances such as poor water resistance or lack in workability despite they can improve properties, if any. Consequently, strong demands have been made on improvement of shrink properties and particularly on impartment of flexibility to molded articles while maintaining the characteristics of the aminoplast resins.
Accordingly, it is an object of the present invention to provide a thermoplastic resin as below and a method for producing the same. The thermosetting resin in question is very stable, can optionally be diluted with water before use with good workability, has high stiffness and chemical resistance that are advantages of aminoplast resins, has water resistance and high strength at high humidity, has improved brittleness, which brittleness is a disadvantage of the aminoplast resins, and thereby has excellent flexibility and impact resistance, and has excellent adhesive force in water. Thus, the thermosetting resin can advantageously be used for resin impregnation and as an adhesive for use in building materials.
The present invention provides:
[1] A thermosetting resin including a methoxylated alkaline-condensation product, the alkaline-condensation product including:
5% to 95% by weight of an aminoplast resin (A) (solid content); and
5% to 95% by weight of a polyalkylene glycol (B) (solid content);
[2] a method for producing a thermosetting resin including the steps of subjecting an aminoplast resin and a polyalkylene glycol to a condensation reaction under alkaline conditions to yield an alkaline-condensation product, methoxylating the alkaline-condensation product with methanol to yield a methoxylated product, and controlling pH of the methoxylating product in a range from 10 to 11;
[3] the method for producing a thermosetting resin as set forth in [2] wherein the aminoplast resin (A) is at least one selected from the group consisting of melamine-formaldehyde resins, melamine-glyoxal resins, urea-formaldehyde resins, urea-glyoxal resins, carbamide-formaldehyde resins, benzoguanamine-formaldehyde resins, and glycol-urea resins;
[4] the method for producing a thermosetting resin as set forth in [2] or [3] wherein the polyalkylene glycol (B) is polyethylene glycol or polypropylene glycol;
[5] the method for producing a thermosetting resin as set forth in any one of [2], [3] and [4] wherein 100 to 500 parts by weight of methanol is added to 300 parts by weight (solid content) of the alkaline-condensation product between the aminoplast resin and the polyalkylene glycol to thereby methoxylate the alkaline-condensation product;
[6] a method for producing a molded thermosetting resin, the method including the steps of adding a strongly acidic catalyst to the thermosetting resin as set forth in [1], impregnating a reinforcing material or a filler with the resulting mixture, and heating the impregnated article at 120xc2x0 C. to 180xc2x0 C. under a pressure; and
[7] the method for producing a molded thermosetting resin as set forth in [6] wherein the molded thermosetting resin is any one selected from decorative laminated sheets, WPC (wood-plastic combination), heat-resistant inorganic boards and center materials used for making tatami mats.